1. Field of the Invention
The present invention relates to a polymerization processor for synthesizing a polymer from a polymer raw material in a molten state.
2. Description of the Related Art
Synthesis of a polymer by a ring-opening polymerization reaction may have a problem of degradation in quality such that the polymer is in part thermally degraded and colored due to prolonged temperature history and accumulation of heat of reaction associated with polymerization.
Polylactic acid, which is one of polymers synthesized by the ring-opening polymerization reaction, is a colorless and transparent polyester prepared using lactic acid being a biomass as a raw material. Methods for synthesizing polylactic acid from lactic acid includes a method in which lactic acid is condensed to produce an oligomer, a catalyst such as antimony oxide is added to the oligomer to carry out depolymerization to produce lactide, and a catalyst such as tin octylate is added to the lactide to carry out ring-opening polymerization. In this case, polylactic acid may be in part thermally degraded and colored due to a rise in temperature associated with heat of reaction during ring-opening polymerization. It is desired that the coloring is inhibited because it impairs colorlessness and transparency which is one of the characteristics of polylactic acid.
Thus, in the invention described in JP Patent Publication (Kokai) No. 8-259676A (1996), a continuous polymerization in which a plurality of reaction tanks for ring-opening polymerization of lactide are prepared, and the reaction tanks are connected in series to supply a raw material and discharge a polymerized product at the same time is employed, and operations are carried out with temperature, the concentration of catalyst and retention time varied for each reaction tank to alleviate thermal degradation due to temperature history. In this system, however, factors contributing to coloring such as (1) prolonged temperature history resulting from variations in retention time due to mixture of a polymer having a low polymerization degree and viscosity and a polymer having a high polymerization degree and viscosity and (2) acceleration of thermal degradation associated with accumulation of heat of reaction associated with ring-opening polymerization reaction, are not eliminated yet.